There is a great commercial need for stringent thickness control of crystalline plating, films, and coatings. The performance of many electronic devices is critically dependent on the film thickness. Significant manufacturing cost reductions and improvements in quality and reliability can be achieved by insuring that the applied film thickness is within the acceptance limits for a specific application.
X-ray diffraction (XRD) techniques enable measurement of the thickness of thin films in a non-destructive, non-contact, and quantitative manner.
Conventional XRD-based film thickness measurement analyzes the attenuation of the diffraction intensity, by comparing the integrated intensity of the incident x-ray with the integrated intensity of the x-ray diffracted from the films themselves or from the films and the substrate, according to the kinematical expression of the integrated diffraction intensity.
J. Chaudhuri (J. Chaudhuri and F. Hashmi, “Determination of thickness of multiple layer thin films by and x-ray diffraction technique,” J. Appl. Phys. 76 (7), (1994), pp. 4454-4456) proposed a technique for determining thickness of multiple heteroepitaxial films deposited on a single crystal substrate, based on the integrated intensity reflected on rocking curve of each film and substrate. Chaudhuri corrects the kinematical expression of the integrated diffraction intensity, by applying the primary and secondary extinction of diffracted x-rays, according to the mosaic crystal model established by C. G. Darwin in Phil. Mag., vol. 27, pp. 315 and 657 (1914) and vol. 43, pg. 800 (1922). The block thickness of such mosaic crystal model was assumed a priori, and the constant referring to block tilts is determined through calibration using a single film with known thickness.
However, the technique disclosed by Chaudhuri applies only to heteroepitaxial films, which are characterized by single crystal-like texture, and is not suitable for determining thickness of a textured polycrystalline film or stacks of films, where the crystallographic texture varies widely and impacts the diffraction intensities differently.
Ruud (C. O. Ruud, M. E. Jackobs, “Method and apparatus for in-process analysis of polycrystalline films and coatings by x-ray diffraction,” U.S. Pat. No. 5,414,747, May 9, 1995) proposed to use multiple position sensitive detectors to register multiple diffraction peaks simultaneously. Specifically, Ruud uses the diffraction intensity of one or more diffraction peaks from the substrate to calculate the thickness of the coating, presumably according to the absorption equations. However, Ruud does not suggest or teach elimination of crystallographic texture effects from the measurements of diffraction peak intensity.
It is therefore an object of the present invention to provide a method for determining thickness of textured polycrystalline thin films, by correcting the diffraction intensity measurement to eliminate crystallographic texture impacts therefrom.
It is another object of the present invention to provide a film thickness mapping system, which rapidly and automatically collects and processes diffraction data for determining thickness of textured polycrystalline thin films.
Other objects and advantages will be more fully apparent from the ensuing disclosure and appended claims.